Current diagnostic methods for detecting damage to heart tissue are based on measurements of serum levels of a number of different enzymes. Each of these is not sufficient to indicate the exact tissue that has been damaged unless the levels are very high. We are proposing to develop a definitive diagnostic test which will be specific for cardiac tissue damage. In addition, the test may be sensitive and accurate enough to detect and quantitate very minor damage to cardiac tissue and possibly be utilized as a routine screening procedure. The rationale for our proposal is based on the fact that there are two forms of a soluble enzyme in rat and rabbit heart tissue which are immunologically distinct. The circulating level of enzyme in human serum is normally almost zero or extremely low and therefore if cardiac damage occurred, the increase over this low background level should be easily detected. We are purifying this enzyme from human hearts and will use it as an antigen to produce monospecific antisera in rabbits. Subsequently, a radioimmune assay will be developed to quantitate low levels of this antigen in human sera and double blind studies will be carried out to assess its usefulness for a routine diagnostic test for cardiac damage.